This list is by no means complete or definitive. There have been many mergers and acquisitions in the history of the electronics industry. For example, Fairchild acquired the Raytheon semiconductor line in 1997, which line included RC and RM prefix ICs. More recently, Intersil acquired the Harris semiconductor line, which line included the old Harris HA series parts found in many logging tools along with the CA series parts found in many Comprobe tools (originally made by RCA and acquired by Harris). Incidentally, Intersil should be lined up and shot for discontinuing the popular CA3094 right after acquiring the Harris line.If you are working with chips, check out the Chip Directory. The Chip Directory and the mailing list associated with it are wonderful resources. More than once the friendly and helpful members of the list have bailed us out of technical difficulty.